The old code would have mandated six emergency exit stairwells in each tower. The Port Authority interpreted the new rules as requiring only three stairwells per tower. However, even under the new code, each tower should have included at least a fourth stairwell,12 to accommodate visitors to public spaces on the highest floors. Also, fire safety experts generally urge that stairwells in tall buildings be spaced as far apart as possible. But in each of the Twin Towers, the three stairwells were bunched relatively close to one another in the central core. That left them collectively more
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